It is an object, according to the present invention, to provide a capacitive discharge ignition system capable of generating an arc discharge between the spark plug electrodes with a duration three to six times longer than typical for the type of ignition coil in use.
It is a further object, according to the present invention, to be able to adjustably and selectively modify or disable the extended duration spark to obtain the best possible spark plug life.
When engine operation conditions require spark durations previously unavailable from capacitive discharge ignitions, the extended spark can be enabled. This allows the use of a capacitive spark ignition system where inductive-type ignition systems were the only practical choice.
Briefly, according to the present invention, there is provided a capacitive discharge (CD) ignition system for an internal combustion engine. The ignition system comprises a storage capacitor and diode in series therewith, a converter transformer having primary and secondary windings, the secondary winding thereof connected in series with the storage capacitor and diode, an ignition transformer having primary and secondary windings, a first triggerable switch, the primary winding of the ignition transformer and the storage capacitor being connected in series through the first triggerable switch, a spark plug connected in series with the secondary winding of the ignition transformer, a source of direct current, and a second triggerable switch connected in series with the primary of the converter transformer. A circuit is provided to control the first and second triggerable switches in synchronism with the engine such that while the first switch is open, the second switch is closed for a period to store energy in the converter transformer and then opened to transfer energy to the storage capacitor followed by again closing of the second switch. The first switch is closed to discharge the storage capacitor to the primary of the ignition coil. The second switch is reopened to transfer energy stored in the converter transformer to the primary of the ignition transformer to prolong the current in the secondary of the ignition transformer. The number of times N the second switch is reopened and closed and the time period T for which the second switch remains closed is controlled to control the duration and amplitude of the extended arc current.